1

I think, that notifications should have two new features:
1) Keep in history
Sometimes low priority notification was shown. I may to close it or keep stay above window. There should be new option: hide into notification area/history. Sometimes we could separate source of notification. For example: we could have timer plasmoid in plasma desktop. We could have many of them. How to allow plasma discover if notification comes from specific timer plasmoid or other plasmoid? Solution is simple: made each plasma's notification stay at top until forcibly closed or send to notification history area.
2) Add notes to notification - it will connect with 1) . Sometimes I do not have time to react on notification already, but I need to wrote some though. For example: someone send me message to IM. I do not have time to answer already, but decided to wrote though, what should I say (it would not be fully constructed response, but some point of ordered list of what would I tell). Once wrote notes about dialog with person, whom I talked, I can send notification with notes to history. Another example could be thing to do, when some process completed. I have notification with progress about system update. I add sentence: "close system after done" in notes.